Railroad systems use signals to indicate when a train may proceed safely or when it is required to stop. In the typical railway system electrical circuitry is relied upon to sense the presence of trains. The presence or absence of a train in one location triggers signals in other locations on the system. In many such signal systems electrical current is directed through sections of the track upon which the train rides, so that each section of track defines a portion of an electrical circuit. The presence of a train upon a section of track causes the circuit in which that track is included to short circuit. Signals, such as arrays of light or other visual indicators appropriately located throughout the system, respond to the short with the proper signal display. The signal displays through the system will change appropriately as the train moves through successive circuits.
As a simplified example, when no train is present upon a section of track, the circuit of which said track is a part, will cooperate with the light display or other visual indicator to provide a signal to approaching trains that they are permitted to proceed. On the other hand, if a train is present on a section of track, a short circuit will result that provides a signal which directs approaching trains not to proceed. An actual signal system used in railway operations, of course, is substantially more complex than this example. However, the signal systems employed in many railway operations employ the general principle of incorporating sections of rail into electrical circuits to detect the presence of trains, and in turn, to operate displays of signals.
The length of sections of rail that are incorporated into a signal circuit would vary according to operating speed of the system, alignment and geometrics of the track, operating characteristics of the equipment, visibility and other factors. As an example, however, the signal systems employed in many passenger subway operations are based upon circuits incorporating one thousand foot long sections of track. In certain areas of these subway systems, such as on curves, the signal circuits may be reduced in size to incorporate five hundred foot long sections of track or less.
It is essential that adjacent signal circuits be insulated from one another to avoid unintended short circuits that could cause an incorrect display of signals. Specifically, if the section of track in one signal circuit inadvertently is connected electrically to the section of track in the adjacent signal circuit, an incorrect control signal will result. In the typical railway operation this incorrect signal will be interpreted by the electrical circuitry as a train present on that section of track. Consequently, the signal circuit will trigger a signal display that will require approaching trains to stop.
To avoid shorts, adjacent signal circuits are insulated from one another. Specifically, end posts made of electrically non-conducting material such as polyurethane are placed between the rail sections of adjacent circuits. A typical end post is a planar member having a plan configuration substantially identical to the cross section of the rails. The joint bars that are used to securely connect adjacent sections of rail are partially wrapped in a flexible insulating fabric to further inhibit short circuits across the adjacent sections of rail, and insulating bushings are used to surround the bolts that extend through the joint bars and rail sections.
The standard end post used to separate rail sections in adjacent signal circuits is constructed from a plastic or polyurethane material having a thickness of approximately 3/8 of an inch. It has been found that end posts having a thickness of 3/8 of an inch or less will not directly support the weight of the train riding on the track. Rather, the weight of the train as transmitted through the wheels will be supported mostly by adjacent sections of track. However, as the thickness of the end post increases above 3/8 of an inch, the proportion of the train weight carried by the structurally weak end posts also increases. As a result, end posts having a greater thickness are likely to wear very quickly, and in some circumstances to fail entirely. The wearing of thick end posts results in the end post assuming a concave or dish shaped configuration. Consequently, train wheels will not roll smoothly over these joints, but will abruptly contact the adjacent rail section. This abrupt contact across the discontinuous joint significantly affects the life and performance of the equipment riding on the track, and can cause failure of the joints between adjacent rail sections.
Although the end posts having a thickness of 3/8 of an inch provide a long lasting mechanical connection, they are not particularly effective insulators. Specifically, the continuous movement of the heavy railway equipment over the rails causes metallic flakes to become separated from the rails. These metallic flakes and other electrically conductive dust particles in the railway system environment collect on the rails in the vicinity of the end post. This collection of metallic particles in the vicinity of the end post is encouraged by the weak magnetic field that is generated by the signal circuits in the adjacent rails. After a period of time, these electrically conductive metallic particles may extend across the end post bridging the gap between adjacent signal circuits. A short circuit will result from this continuous collection of metallic particles across the end post thereby resulting in the generation of an incorrect control signal.
In the typical railway system, the short circuit resulting from metallic particles bridging the gap established by the end post will result in a signal display that requires approaching trains to stop even though it is in fact safe for the trains to proceed. Typically, this signal malfunction can be corrected only by first locating the problem and then dispatching a maintenance crew to the area to eliminate the short circuit. This, of course, is time consuming and costly, and results in residual effects on the operation of trains throughout the entire railway system. It is estimated that in the New York City subway system, for example, signal malfunctions of this type occur several thousand times each year with a resultant substantial effect on the operation of the entire system.
Attempts have been made to increase the thickness of the insulated joints between adjacent signal circuits to minimize the possibility of electrically conductive particles bridging the gap established by the end posts. However, as explained above, these thicker insulated joints have resulted in mechanical deficiencies with long term operational effects that are at least as serious as the electrical malfunctions described above.
In view of the above, it is an object of the subject invention to provide an improved insulated joint between the rail sections of adjacent signal circuits.
It is another object of the subject invention to provide an insulated joint between rail sections of adjacent signal circuits that minimize the occurrence of short circuits.
It is an additional object of the subject invention to provide an insulated joint between rail sections of adjacent signal circuits that is capable of physically withstanding the forces exerted upon the connection during the operation of the railway system.
It is a further object of the subject invention to provide an insulated joint between rail sections of adjacent signal circuits that will assure an adequate mechanical connection between the rail sections.
It is still another object of the subject invention to provide an insulated joint between adjacent sections of rail in a signal circuit that is inexpensively manufactured and easily installed.